Effect of nano-YSZ and nano-ZrO2 additions on the strength and toughness behavior of self-flowing alumina castables

Abstract

In this work, a novel composition of self-flowing, ultra-low cement (ULCC) tabular alumina-based castables is developed. Ultra low cement castables (ULCC) are processed using various amounts (5, 3, 1, 0.1 and 0.01wt%) of nano-ZrO2 and yttria-stabilized zirconia, (YSZ) and then sintered at different temperatures up to 1773K. In addition, binding systems without aggregates with varying yttria contents (1, 2, 3 and 8mol%) and stabilized ZrO2 are sintered at 1273K, 1573K and 1773K for 3h. In order to disclose the effect of nano-ZrO2 additions, firing temperatures, and corresponding phases, present in the castables are investigated using dynamic light spectroscopy (DLS), X-ray diffraction, scanning electron microscopy (SEM), fracture toughness, and three point bending (MOR). DLS results show that the nano-ZrO2 particles are effectively distributed in the matrix using either additives or ultrasonification. It is found that the addition of 3wt% nano-ZrO2 improves the MOR of self-flowing castables (SFCs) by 20% and 50% matrix and binding systems respectively due to stabilization of t-ZrO2. Alternatively, there is no noticeable change in the exhibited KIC of castables when aggregates are present. In contrast, the KIC of aggregate-free binding systems can reach values of up to 2.27±0.21MPam1/2 with the addition of 1wt% Y-ZrO2. The experimental outcome indicates that the presence of alumina aggregates in the SFCs leads to excessive porosity and inherent flaws in the binding regions when the refractories are fired at high temperatures. Consequently, the effect of nano-YSZ in promoting toughness is significantly reduced or eliminated due to the presence of high porosity and internal flaws in the SFCs.